The invention is based on a valve for controlling fluids as generically defined by the preamble to claim 1.
From European Patent Disclosure EP 0 477 400 A1, an arrangement for a valve of this generic type is known in which the deflection of the piezoelectric actuator is transmitted via a hydraulic chamber. An adaptive, mechanical tolerance compensation, acting in the stroke direction, for a travel transformer of the piezoelectric actuator is provided.
In the known arrangement, the hydraulic chamber functions as a so-called hydraulic step-up means. The hydraulic chamber encloses a common compensation volume between two pistons defining this chamber, of which one piston is embodied with a smaller diameter and is connected to a valve member to be triggered, and the other piston is embodied with a larger diameter and is connected to the piezoelectric actuator.
The valve member, piston and piezoelectric actuator are located one after the other on a common axis.
The hydraulic chamber is fastened between the two pistons in such a way that the actuating piston of the valve member, which piston is retained in its position of repose by means of one or more springs relative to a predetermined position, executes a stroke that is increased by the step-up ratio of the piston diameter when the larger piston is moved a certain travel distance by the piezoelectric actuator.
The compensation volume of the hydraulic chamber makes it possible for tolerances caused by temperature gradients in the component or different coefficients of thermal expansion of the materials used and possible settling effects to be compensated for without causing a change in position of the valve member to be triggered.
Compensating for changes in length of the piezoelectric actuator, the valve member or the valve housing by means of the hydraulic chamber disposed between two pistons requires a complicated construction, however, and is problematic in terms of the incident leakage losses and the refilling of the hydraulic chamber.
From German Patent DE 196 46 511 C1, a drive or adjusting element of the piezoelectric actuator type is known which is used to generate tilting motions in high frequency ranges. In the drive or adjusting element, a first and a second region of piezoelectrically active material are provided, these two regions communicating with one another via a third region. The third region is of piezoelectrically passive material. Applying a voltage, for instance to the first region of the drive element, correspondingly expands this region expanded in its longitudinal direction, resulting in a corresponding bending along the axis of symmetry of the entire piezoelectric drive element. A reversal of the bending or tilting angle of the drive element can be achieved by applying a voltage to the second region of the drive element.
The object of the invention is to create a valve for controlling fluids in which an arrangement with a piezoelectric unit and a tolerance compensation is provided that has a simple structural design with as few components as possible and requiring little space.
The valve for controlling fluids of the invention as defined by the characteristics of the body of claim 1 has the advantage that by the cooperation of the control member and the piezoelectric unit, triggering of the valve is achieved without an additional tolerance compensating element for elongation tolerances, in particular temperature-dictated elongation tolerances.
In the valve of the invention, the control member acting as a lever arm is connected to the piezoelectric unit in such a way that when electric current is imposed on only one piezoelectric actuator, the control member is tilted relative to its longitudinal direction by the resultant lengthwise expansion. Thus in a sense the control member acts as a tilt lever. Depending on the direction of tilt of the control member, the valve member connected to the control member is correspondingly moved in the longitudinal bore of the valve body. The valve member thus executes a reciprocating motion, as a result of which the valve is put into the closing or opening position.
As a result of temperature changes, both piezoelectric actuators expand approximately equally, so that the control member, which is disposed approximately at a right angle to the direction of motion of the valve member, advantageously causes no reciprocating motion of the valve member. Thus temperature-dictated elongation tolerances, in particular, have no influence on the control of the valve.
Because in the valve of the invention it is possible to dispense with an additional temperature compensating element, an advantageously simple structural design of the valve is possible.
The valve of the invention is especially well suited to use as a fuel injection valve. However, it is understood that still other fields of use are possible, in which valves with high frequency triggering are required.
Further advantages and advantageous features of the subject of the invention can be learned from the description, drawing and claims.